ASPIRANT - assessing the present and future changes of marine climate extremes at the eastern boundary of the South Atlantic off Angola

• Applicant: Rodrigue Anicet Imbol Koungue, Ph.D.
• Subject Area: Oceanography
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511812462

The tropical Angolan upwelling system located in the southeastern Atlantic hosts an area of enhanced biological productivity and important fisheries. With the ongoing global warming, between 1982 and 2018, the sea surface temperatures (SST) off Angola have increased by 1.5˚C to 2˚C resulting in the disappearance of around six to seven local species of fishes. In addition, every few years, warm tropical waters intrude into the tropical Angolan upwelling region resulting in a decrease of local fish stocks and enhanced local rainfall. These extreme warm events are called Benguela Niños and their cool counterparts Benguela Niñas. They are associated with local and remote forcing mechanisms. We have shown that these forcing mechanisms undergo multidecadal variations with a reduced influence of the remote forcing between 2000-2017 relative to 1982-1999 resulting in a weakening interannual SST variability over the Angola Benguela Area (10˚S-20˚S, 8˚E to the coast) in the post 2000 period. Moreover, simulations from state-of-the-art climate models also portray a future reduction of the interannual SST variability in a warmer climate in the tropical Atlantic. However, since 2018, two consecutive extreme coastal warm events have been recorded off Angola in 2019/2020 and in 2021 suggesting again an increase of the interannual SST variability which could be in contradiction to the long-term trend found in climate models. In a recent study, we have investigated the 2019 Benguela Niño event and stressed the importance of both local and remote forcing during the event. With the severe impacts on ecosystem and fisheries, it is of tremendous importance to investigate if we are again changing into a state with an increased frequency of extreme warm events off Angola. The principal goal of ASPIRANT is to assess the present and future changes of the interannual variability off Angola. The specific objectives are: (1) to understand the physical forcing of the 2021 extreme warm event and its impacts on the marine ecosystem along the Angolan coast; (2) to disentangle the role played by the local and remote forcing in driving eastern boundary thermocline and circulation variability off Angola and to assess the long-term variability and trends in the different underlying local and remote forcing mechanisms; (3) to assess the ability of climate models such as the Flexible Ocean and Climate Infrastructure (FOCI) model, the Coupled Model Intercomparison Project phases 5 and 6 (CMIP5, CMIP6) and the Norwegian Earth system models (NorESMs) in simulating the extreme events and trends off Angola and advise on model improvements. If funded, ASPIRANT will offer a better understanding of the physical forcing of the ocean variability off Angola and the implications for the marine ecosystems. ASPIRANT will significantly contribute to the European project TRIATLAS whose goals are to enhance our knowledge on the current state and future changes of the Atlantic marine ecosystems.

• DFG Programme: Research Grants